The need for energy is a major issue throughout the world today. As compared to petroleum sources, fuels derived from biological organisms (biofuels) can be potentially obtained in a more environmentally sustainable fashion. For example, the use of algae as a source of biofuel production has gained enormous research interest. Algae can use photosynthesis to convert carbon dioxide to lipids and hydrocarbons, useful as biofuel with or without further processing beyond the initial extraction. Algae are also valuable as a food source, as well as a source of other valuable materials, including vitamins, color pigment, essential fatty acids, amino acids, pharmaceutically active substances, and other chemicals. Algae can be cultivated in aqueous conditions of both freshwater and seawater. Algae can grow very quickly, and have been known to double their biomass in 24 hours. Algae can be grown year-round with much less land-demand than conventional agriculture.
An important step in the derivation of fuel or other products from algae, as well as in water-purification processes, is the sequestration of algae from a liquid medium. Methods of separating algae from water include, for example, coagulation, flocculation, flotation, centrifugation, filtration, and gravity sedimentation. However, these methods often suffer from expensive inefficiencies due to the nature of the separation. For example, methods of sequestering algae from water using filtration generally have the disadvantage that algae tends to block the filter over time, requiring large amounts of pressure and energy to force the media through both the filter and the accumulating algae. Additionally, cleaning microorganisms from a filter can be time consuming and difficult, and the process of recovering the microorganisms from the filter can be fatal to the microorganisms. Algae has a density very close to that of water, and is small with a typical cell size of from 3-30 μm in diameter. The volume of water from which algae is to be separated can be very high.
The separation of algae from water can be time and energy intensive, and can serve as an economic bottleneck to the use of algae as a biofuel source and to the efficient purification of drinking water.